phonography.org.uk

This is my technique for making binaural microphones. Using this technique you can make a set for about £3. This set is designed to be worn in the ear like earbud headphones so they are very stealthy but will pickup slight head movements.

Ingredients for creating your own homemade binaurals

You will need the following items.

• Two omni-directional electret condenser microphones
• One pair cheap in-the-ear headphones

The following items are optional.

• One pair of matched omni-directional electret condenser microphones
• Shrink sleeving
• Glue - epoxy resin or rubber glue

Sound Samples

Sourcing the microphones

The electret condenser microphones came as a job lot via ebay. I paid about £10 for 25 microphones.

Matching the microphones

I don't have the equipment to measure the response of microphones so I measured the resistance of each unit in a quiet room using a Digital Multimeter. I don't suppose this is a very accurate a method but it was all I could think of at the time and has been OK for me since. This gives me a rough indication of 'similar' not perhaps 'matched'.

Earbuds

I went to Asda and bought 5 pairs of 99p headphones. This gives at least 4 trial efforts before the last pair and allows you to try your best to 'match' them into pairs. The units were in 'Maganvox' branded blister pack but branded 'Philips' on the plug jack moulding - other brands are available for the same price. The cheaper units seem to be better for both dismantling and soldering as they don't tend to use coated braids for the actual wiring. It doesnt really matter who made them as long as when you have dismantled them you can find enough space for he microphone.

Preparing the earbuds

The earbuds will need to be dismantled as far as removing the driver unit. This will leave wiring for attachment of microphones. The picture on the left shows what these earbuds look like when the external cap has been removed and the driver unit leavered out. When you get this far with both earbuds you will notice the two wires per unit will have different colouring - usually copper colour for the common (or ground connection) and coloured for the line connection. These units were coloured green and red.

Now remove the driver units. You will need a very hot iron and a short dab of the iron tip onto the solder connection. Be careful of the iron being magnetically stuck to the unit as you do this. If I still had the equipment I'd next clean up the joint with a brush and some alcohol, remove the old solder and re-tin.

Preparing the microphones

Take your microphone pair and identify the common connection terminal. This is usually easy to spot and is the terminal that joins to the case or can. If you can't visually identify this then using a Multimeter in turn across each terminal and case, find the terminal with least electrical resistance. Looking at the photo, left, you can see the right hand terminal connected to the case (in this example, three weblike connections).

Attaching the microphones

All that is required now is to solder on the microphone caps. Connect the copper coloured common connection to the case. If you are feeling a little unsteady whilst soldering you might like to use a headsink device around the unit to prevent damage. Reconnect the line connection. You could add a couple of short pieces of shrink wrapping alog the flying leads to prevent short circuiting but this is not usually necessary with modern coated braiding.

Re-assembly

Now its time to put it all back together. If your earbud casing is large enough you can push the caplet back into the case and put the lid back. You may also want to back the cavity to prevent noise from the caplet moving around inside. The foam covers that come with earbuds are ideal for this and offer a minute amount of protection against wind noise.

All that remains is to replace the cover and fix. You can use a small amount of glue for this job or touch on a hot solder iron tip on the joints to give a mechanical heat seal. I must admit that although the heat seal approach is messy it does offer a better seal and stop creaking noises from areas that have not been glued.

Enhancements

Enhancements I have made to these units in the past.

• Seal cable entry point using rubber glue - this gives a good seal and offers flexibility. Also easy to remove if you need to rework the unitis.
• Earbud Winder - Buy a cheap set of earbuds that come with a winder and case. Paradoxically, the more expensive the earbud, the less suited they are to becoming hosts to binaurals.

Binaural sound samples

Binaural sample recorded on the London Underground between King's Cross and Euston Square. Sound is untreated apart from a little amplification.
homemade binaurals -> Zoom H2 -> Audacity -> VBR MP3

Link to the binaural sample

Binaural sample recorded on the London Underground.
homemade binaurals -> Zoom H2 -> Audacity -> VBR MP3

Link to the binaural sample

Binaural sample recorded at King's Cross Station ticket barriers. Sound is untreated apart from a little amplification.
homemade binaurals -> Zoom H2 -> Audacity -> VBR MP3